Apparatus for transferring material



Oct. 5, 1937. J. A. FLINT APPARATUS FOR TRANSFERRING MATERIAL Original Filed May 26, 1934 2 Sheets-Sheet 1 [/YVENTOE James A. F///77 BY 0 4 m M I ATT'Y.

Oct. 5, 1937. J. A. FLINT APPARATUS FOR TRANSFERRING MATERIAL Original Filed llay 26, 1934 2 Sheets-Sheet 2 [N VEN TOR James A. F// '/77 ATT'X Patented Oct. 5, 1937 UNITED STATES 2,094.69! APPARATUS FOR TRANSFERRING MATERIAL James A. Flint, Upper Arlington, Ohio, assignor, by mesne assignments, to The Traylor Vibrator Company, a corporation of Colorado Application May 26, 1934, Serial No. 727,770

. Renewed July 20, 19:7

7 Claims.

, The present invention relates to a conveyor of the vibratory type. It relates more particularly to a means for conveying granular material such as ore, coal, coke, chemicals, sand, gravel, stone,

cinders and numerous other materials of this general type.

An object of the invention is to provide a conveyor of the above mentioned type in which an electric vibrator is provided which may be varied to control the amplitude of vibration and consequently the delivery rate of said conveyor.

Other objects of the invention will appear hereinafter, the novel features and combinations being set forth in the appended claim In the drawings:

Fig. l is a side elevation of my invention; Fig. 2 is a plan 'view thereof with the conveyor trough removed;

Fig. 3 is a rear end view of my device; Fig. 4 is a side elevation of one form of trough or pan;

Fig.5 is an end view of the trough of Fig. 4; Fig. 5 is a side elevation. of another form of trough; Fig. 7 is an end view of the trough of Fig. 6;

Fig. 8 is a side elevation of still another trough in the form of a cylinder;

Fig. 9 is an end view of the cylindrical trough of Fig. 8, and I Fig. 10 is a section on line l0|0 of Fig. 8

looking in the direction of the arrows.

Referring to the drawings, there is'seen at 20 a base for my conveyor preferably comprising a rather heavy metal member, for example an iron 3 or steel casting. Said base 20 may be provided with a hollowed portion 2| to reduce its central weight and is preferably formed solid at its rear end 22 to provide maximum weight at this point, for a purpose hereinafter set forth. Said base 20 is provided with feet 25 of any desired material, for example soft rubber, secured to the base by any desired means, as screws. If desired the feet 23 may be eliminated and the base 20 provided with brackets for attaching it rigidly to any-frame or sub-base.

Carried upon the base 20 are a plurality of cantilevers 24, 25 and 26. Three such cantilevers are employed inthe device illustrated but any number may be employed so long as the hereinafter discussed relation is maintained. The cantilevers 24, 25 and 26 preferably comprise metallic plates, such as steel plates, rigidly attached at one end to the base plate 20, as by screws 21 and clamping bars 26.

Carried by the cantilevers 24, 25 and 26 ad.

cent their upper ends is a material supporting member comprising a trough or pan It. This trough or pan 30 may have any desired sectional shape, and in any case is preferably provided with a relatively smooth supporting surface 2|. 5 Said pan or trough is rigidly attached to the upper ends of cantilevers 24, 26 and 26 by any desired means, such as screws 32 and clamping bars 33. It is obvious that the cantilevers 24, 25' and 26 provide a support for the trough or 10 pan 30. In addition, said cantilevers are adapted to store energy under the influence of some deflecting means and to transfer said energy to the pan or trough 30, to impart movement thereto, which movement will cause the movement of 15 any material carried by said pan or trough 30, by imparting an impact thereto- It is to be particularly noted that the cantilevers 24, 25 and 26 do not form a right angle with the supporting surface 3i, but each is lo 20 cated in a transverse plane at an angle less than ninety degrees relative to a horizontal plane. This angle may be varied within wide limits but is preferably greater than 45 degrees and less than 80 degrees. It has been found in practice 5 than an angle of 70 degrees is very satisfactory.

Before going further with the mechanical description of the device, it is believed in the interest of a clear understanding of my new method of operation, to consider at this time the meth- 30 0d of operation whereby material is conveyed by said device.

Applicant has a particular theory as to why the conveying action takes place but it is to be understood that he is not restricting his method or 35 apparatus to any theory. Regardless of any theory, correct or not, it is known by applicant that when certain definite steps are -performed, or applicant's particular apparatus is operated, a conveying action is obtained." 40

The cantilevers 24, 25 and 26 not only provide a support for the trough or pan 30 but also comprise energy storing means which energy is em played to impart movement to said trough or pan 30. By deflecting the cantilevers 24, 25 and 26 to the right, as viewed in Fig. 1, energy is stored therein. This deflecting action may be supplied 7 by any desired motor, preferably an electric motor. However, the motor employed should have the characteristic of releasing the cantilevers after they are deflected whereby the energystored therein by their deflection may be utilized to impart movement to the trough or pan 30'. It is believed to be essential that this movement shall have a directional component parallel to the plane that the parallel component be the greater of the two. To obtain these particular components,

cantilevers 24, 25 and 26 are set at an angle to the plane of the supporting surface 3|, as above set forth. It'is applicant's belief that when the supporting surface 3i receives movement, as above indicated, it imparts a force or impact to each particle of material resting on said surface. This force has two components, one parallel to the supporting surface and one perpendicular therewith. The perpendicular component tends to lift the particle off the supporting surface and the parallel component tends to impel it to a position horizontally removed from its first position. The expression "horizontally removed does not require that said movement be restricted to a horizontal plane but means that the movement has a horizontal component. It may also have a vertical component, for applicants device is operative to move material up a grade. That is, the plane of the surface 3| may be inclined to the horizontal and material may be moved up the incline. This feature is of particular importance when applicants method is used in a device for screening material, for which purpose it may well be used, and it is desired to have the bedof material to be screened conveyed up an inclined screening surface."

It is preferred that the supporting surface 3i have a periodic vibratory movement, whereby a series of small movements in rapid succession are imparted to the material. This, of course, requires the cantilevers 24, 25 and 26 to be periodically deflected and released, during each deflection of which energy is stored therein, and during each releasing of which said energy is transferred to the supporting surface 3i and ultimately imparted to the material to be conveyed. Under these conditions, it is applicants belief that the particles of conveyed material pass along the trough in a series of hops, actually touching the surface 3i only at intervals. In actual practice evidence to support this belief is found in the fact that highly abrasive materials have been conveyed with little wear on the supporting surface 3i even after extended use. Where the material comprises particles forming a bed of relatively small particles, the particles at the top of the bed may never touch the supporting surface 3i, but they will be impelled by being struck by the particles of the lower part of the bed, and therefore thick beds of material may be conveyed as well as thin beds.

It is conducive to increased efiiciency of operation, to make the rate of oscillations of the supporting surface 3| high. Applicant has employed with success vibratory frequencies between 3000 cycles per minute and 7200 cycles per minute.

In order to enhance greatly the efiiciency of applicants method and apparatus and to reduce greatly the energy necessary to efiect said method it is extremely desirable that the vibratory system, which may be considered as comprising the pan 30 and all elements rigid therewith, including approximately one-third of the cantilevers 24, 25 and 26, comprise an oscillatory system the natural period of vibration of which is substantially equal to the period at which said body is vibrated by the operating motor. However, it is preferable that the period of vibration of said body be not exactly in resonance with the frequency of operation of said motor for such a condition tends to render the device unstable. As is well know portionate.

when a body is vibrating at its natural period, the only energy necessary to maintain said vibration is that required to supply the losses.

Furthermore, said oscillations are easily damped out if the supplied energy is reduced to prevent self destruction, by placing a light load on the device. To provide prope control and yet receive a considerable advantage inherent in operating the vibratory system at its natural period I prefer to operate said system at a period slightly different from its natural period. In this manner the system is always loaded to some degree, thereby preventing self destruction and providing proper control. This may be done by operating said systemat a period either slightly lower or slightly higher than said natural period.

In practice, a difference of from one-fourth to five (5) cycles above or below the natural period is employed and this range is intended in any claim which requires the operation of the unit at a period which differs slightly from the natural period thereof. In smaller size units, the lower part of the range is used and in a typical illustration it will be from one-fourth A) to one and one-half (1%) cycles of]? of resonance for a 60-cycle unit. In the larger size units, the higher part of the range is employed and in a typical illustration it will be from one and one-half (1 to five (5) cycles off of resonance where the machine is energized at 60 cycles. The larger the machine, the farther it will be operated from its resonant frequency. For frequencies other than 60 cycles, the setting off of resonance will be pro- These settings may be either above or below resonant frequency, as was previously mentioned. In practice it has been found desirable to construct the device for operation at a frequency slightly higher than its natural period. If a person in using the device should find that its maximum delivery was less than desired it might then be increased by slightly decreasing the period of said system. This decrease in period may be accomplished by slightly releasing the rigidity of one of the cantilevers, for example by loosening one or more of the screws 21 to a slight extent. If for reasons of safety, it is desired toprevent the system from being tuned to its exact natural period, after being once constructed, said system may be constructed with a natural period slightly below the period at which it is to be operated.

It is to be noted that when the cantilevers 2d, 25 and 2B are deflected to store energy and thereafter give up or dissipate said energy, not

only do they exert a force on the pan or trough 30 but they also exert a force on the base 20. It is, of course, desirable that said stored energy be employed to a maximum degree in imparting motion to the pan or trough 30 rather than to said base 20. This is effected by the fact that the pan or trough, and such elements as are rigid therewith have the above mentioned natural period close to that of the period of vibration imparted thereto, while the base 20, and the parts rigid therewith, are not resonant at this period. In addition, the base 20 is made considerably heavier than the pan or trough 30. In theory, it might well be of infinite weight. In practice, it has been found desirable to make it at least twice as heavy as the pan or trough 30.

Furthermore, to derive the maximum benefit from the forces created by cantilevers 24, 25 and 26 when they give up their stored energy it is preferred that the resultant of all of the forces of these cantilevers pass through the center of percussion of the vibratory system; that is, the

pan II and its rigid elements. As is well known. a force applied at the center of .percussion of a mass will impart the maximum acceleration thereto. In addition, the most emcient distribution of the energy given up by cantilevers ll, 25 and 2!, as between the vibrating system and the relatively stationary system including the base 20. would be effected if the resultant force, above mentioned, not only passed through the center of percussion of the former but also passed through the center of gravity of the latter. To accomplish this result it would be necessary to extend the base 20 rearwardly, and in some cases this is possible. In general, however, satisfactory operation is accomplished by concentrating the weight of the base near the rear end thereof as much as possible. This is done by removing base material near its center and making the rear end 22 solid..

Purely by way of illustration, and not by way of restriction, applicant submits herewith an example of one method of designing a typical conveyor which .has been found operative and also submits some of the constructional details thereof.

Assuming it is desired to construct a conveyor with a trough or pan (deck). having a flat burden supporting surface totransport 2000 pounds of silica sand per hour over a distance of 15 inches.

The size of the trough or pan (deck) is first determined, such as the width and depth. For

example the desired width may be 3 inches.. The

depth will then be computed as follows:

Wm=2000 lbs. per hour. Vm=2000/SPC1flC weight expressed as lbs. per cu. ft.

In this case, silica sand having a specific weight of 100. V

V,,,- -20 cu. ft. per hr.

Assume a conveying speed (Cm) of 1200 feet per hour, which is a practical speed as determined by experiment where dm=depth of burden in inches W=width of deck in inches Am=cross sectional area of burden expressed in sq. inches.

Wn=weight of burden delivered in pounds per hour Vm=Volume of burden delivered in cu. ft. per

hour terials of lighter weight.

' The deck is then designed, as to general shape, etc., within the above noted limitations and the material thereof selected. This material may be almost any suitable metal such as steel, aluminum, brass, wood, glass, etc.

The weight of the deck is then approximately determined by the dimensions and the material used, within reasonable accuracy.

. lbs

From the length of the deck the spacing of the cantilever bars to be employed are determined, to provide uniform movement of each portion of the deck during vibration thereof. In the size deck above mentioned, made of aluminum, the spacing of the cantilever bars should be approximately five inches. Therefore, it is determined that three sets of cantilever bars are to be employed. A set may be one cantilever bar or, if necessary to provide rigidity, it may comprise more than one bar. In the illustrated case, only one bar is necessary for a set. I

The weight of the vibratory system comprising the deck, the vibrating armature, and of each of the vibrator bar clamps is finally determined with accuracy by the cantilever bars.

To select the particular cantilever bars to be used, resort is made to the general formula for computing the load capacity of any single cantilever bar when so functioning. This formula is:

Wc=Kw(Wg-Wb) (2) in which Wc=the effective load capacity, in lbs.

W =the gross load capacity, in lbs.

Wb=the effective vibrating weight of bar, in

Kw==the load factor, an empirical factor determined by experimental methods.

The basic formula by which W. is determined is:

aEbh W for a bar of uniform rectangular cross-section In which a=a numerical constant, different for each type bar. For the cantilever type it is a. constant for any cross-section or for any material.

E=the modulas of elasticity of the material of the bar, in lbs.

h=the width of the bar, in inches.

h=the thickness of the bar, in inches.

L=the vibrating length of the bar, in inches.

n=the operating frequency of vibration, in cycles per second.

For the device under consideration E=30,000,000# (for steel) -==.065" =2%" (selected for trial) n= cycles per sec.

Then

- =.82 lb. We is determined from the general formula d bhL in which db=Spe0ifi0 weight of the material of the bar in lbs. per cu. in.

h=the width of the bar, in inches h=the thickness of the bar, in inches L=the vibrating length of the bar, in inches 2=a numerical constant Then The values of b, h and L are as given above.

db=.288 for steel =.08 lb. (approx.)

Substituting the values of W and We in For mula 2 Kw=.9l as determined by experiment for this type of deck and conveyor.

Therefore each cantilever bar will vibrate a weight of .67 lb. at the rated frequency of 120 cycles per sec.

As three bars are'here employed the weight of the vibrating system will then be 3 x .6? 1b.: 2.01 lbs. If the pan or deck is heavier, then a greater number of bars of this type may be employed or the same number of bars bf greater capacitymay be used.

The motor is then selected with suitable power to vibrate the weight-of the vibratory system. The base plate is then made with a weight of at least twice that of the vibratory system; In this case it would be at least 4 pounds in weight, and preferably 6 pounds.

Other'methods of design may be employed, the fundamental requirement being that the formula Wc=Kw (WgWb) be satisfied for each condition. This, of course, may include almost an infinite number of conditions for practically each of the terms, including E, b, h, n and L and the number of cantilever bars, is a variable.

Returning-to a consideration of the device illustrated in the drawings, and particularly to the motor means for periodically storing energy in the cantilevers 2d, 25 and 26 and then releasing said cantilevers, I have shown an improved motor of the electrical type. It is to be understood, however, that any well known type of electrical or mechanical motor may be employed which will periodically deflect the cantilevers 24, 25 and Z6 and then effectively release them whereby they may transfer their stored energy to the vibratory system.

In the motor illustrated, which is of a new and improved type and embodies a new and improved method of operation, I provide a cradle 46, comprising a base 4! and integral similar U-shaped end brackets 42, '43. The base 4! is rigidly attached to base 29, as by screws 4|. Said end brackets 42 and 43 are each provided with a forward arm 44 and a rearward arm-45. Carried between the forward arms 44 is an inverted U- shaped bracket 46, the opposed legs of which are carried on the opposed forward arms 44, by any desired means, such as screws 41. On the base of said bracket is carried a stationary armature 48, preferably comprising laminations riveted to said bracket base. Directly above the stationary armature 48, but out of contact therewith, is a vibratory armature 49 carried on an angle member 50 in any desired manner, as by rivets; the armature 49 and member 59 being rigidly attached to the pan or trough 30. As illustrated in the drawings, the member 50 may comprise one anchor bar for retaining one of the cantilevers rigid with the pan or trough 30. To this end screws, not shown, may pass through the armature 49, members 59, and cantilever 25 and be threaded into a boss on the pan or trough 30. The armature 49 also preferably comprises a series of laminations.

The rear arms 45 of cradle 40 are each provided with an opening 60 adapted to receive rotatably a shaft 65.

' Said openings 60 may form a split hearing by providing said arms 45 with extendng fingers 62 ings 69 and the friction on shaft ti.

access? to receive an adjusting screw 68. Said screw 69 passes freely from. the rearward arm 62 and threads into the forward arm 62 thus providing means for effectively varying the size of open- This friction is preferably maintained such that shaft Bl may be rotated but when set in one position will remain therein.

Intermediate the arms 45 is provided a supporting plate 70 provided with a lateral bore ii at one end adapted to receive the shaft 66. Said plate I6 is maintained rigid with said shaft fit, for rotation thereby, by the set screws 72 which thread through the rear face of said plate id and impinge the shaft ti. The forward end of plate i9 is provided with a lateral channel to receive and support a W-shaped field core, preferably of laminated construction. Said field core comprises the central core member E5, the side core members 16 and the base core member Tl. Said W-shaped field core is held rigid to said plate 16 by bolts I8 passing through the base ill thereof and through the forward end of said plate opposite said channel.

Surrounding the central core 75 is a coil 88 of insulated wire providing the field winding for said field core. A cable 8! including a pair of insulated conductors leads from said field coil to any desired terminal, such as a plug terminal 82. Said cable may be held to plate ill by means of a clip 83 and to base 2! by a bracket 84. Suit-= able openings are provided in cradle 46 and base 29 to allow passing of said cable therethrough.

Adjacent one end of the shaft N there is provided a handle 90, shown of reduced length in the drawings in the interest of clearness, held rigid to said shaft 6! for rotation thereof. Said handle forms a bell crank lever with an arm 911, the end of which is connected by a clevis to an adjustable throw control mechanism. This mechanism comprises threaded shaft 92 provided with adjustable thumb nuts 93, 94. Said shaft 92 extends loosely through anopening in a lateral extension 95, integral with cradle M.

It will be evident from the drawings that the field core comprising center core 15 and side cores 73 may be positioned opposite the armature 49 or opposite the armature 48 orin anyintermediate position between these two extreme positions. For example, said field core may be bridged half by the vibratory armature 49 and half by the vibratory armature 48. The extreme positions of adjustment possible are variably controllable by the thumb nuts 93, 94. By operating handle 96 the field core is rotated on shaft 6i and may assume any desired position relative to said armatures 48 and 49 and when placed in a desired position is there retained by friction. To insure retention in a fixed position, if desired, thumb screws 93, 94 may be screwed home against the sides of arm 95, as illustrated in the drawings.

By providing the adjustable fieldcore and the two armatures 48 and 49 I provide a very effective means for controlling the amplitude of vibration of. the vibratory assembly without requiring variations in the current of the field coil, which will maintain saidfield current substantially constant. If the reluctance of the magnetic path of the alternating current electromagnet is increased, as by increasing the air gap, the current in the exciting winding will increase to mantain the flux substantially constant.

With the field core opposite the vibratory armature 49' substantially all of the flux passes through said armature 49. This flux is alternating in intensity in step with the current alternations in the field coil. However, the attracting force of said flux has twice the frequency of the field current.

The vibrating armature 49 is located closely adjacent to the stationary armature 48 as shown in Fig. l andboth armatures extend transversely of the supporting structure in front of the forward ends of the poles I5, I6, I6. The air gap between the poies and the armature is therefore approximately uniform irrespective of the position of the electro-magnet. Consequently the choking effect on the current flow is approximately the same whether the poles 15, I8, 16, are facing the armature 49 or facing the armature 48 or are in an intermediate position. The fixed armature 48 is therefore particularly useful in acting as a safety feature in preventing excessive currents in the field coil when the outer ends of the poles are in relatively low positions. Regulation of the amplitude vibration of the deck or trough may therefore be obtained while maintaining the current flow through the electromagnet substantially constant. For example, if the field is excited by alternating current of 60 cycles per second, the armature 49 will vibrate at a rate of 120 cycles per second, because each half cycle of alternation is effective to attract said armature. This attraction of the armature 49, of course, results in the deflection of the cantilevers 24, 25 and 26, storing energy in each of them. When the flux is cyclically reduced due to the cyclic reduction in current the deflecting force is gradually reduced to zero. This reduction in force efiectively releases the deflected cantilevers 24, 25 and 26 which restore and transfer their stored energy to the vibrating assembly including pan or trough 30. It is obvious that any source of undulating or pulsating flux may be employed to vibrate the vibrating assembly, of which pulsating direct current as obtained from rectifiers, or any equivalent device, is an example. The principal consideration is to maintain the frequency of the vibrations imparted to the vibrating body, substantially equal, but preferably not exactly equal, to the natural period of said body. Within this limitation, the frequency of the motor and the natural period of the vibratory body may vary as desired. However, as above set forth, a relatively high frequency is preferred.

To reduce the amplitude of vibration of the vibratory assembly, and consequently reduce the rateof delivery of the material, the field structure is rotated counter-clockwise from the position illustrated in Fig. 1, which is the position for maximum amplitude of vibration. This movement results in a gradual division of the total flux in the field core, which total flux is substantially constant, as aforesaid, the stationary armature 48 gradually carrying more of said fiux and thus the vibratory armature 49 carrying less thereof. With the field core substantially opposite the stationary armature 48 no substantial vibrations will be imparted to the vibratory system. Any desired amplitude of vibration between the two extremes is thus possible by establishing a fixed relation between the field core and the two armatures 48 and 49.

As viewed in Fig. 1 the right-hand end is the feed end and the material is discharged from the left-hand end. It has been found in practice that uniform delivery may be relied on although the feed may be variable. It has also been found in practice that the power-consumption of the electro-magnet relative to the work done by the conveyor is relatively low which is believed to be due to the vibratory cantilever action embodying my improved method above described and to the fact that regulation of the amplitude of vibration to vary the rate of feed,,may be had according to the load while keeping the current flow substantially constant.

It is to be understood that the material to be transferred may vary widely as to size and size range. For example, the material may be very finely divided material, in powdered form, or may be very large, such as large rocks, slabs of concrete, pieces of metal, etc. Furthermore, any particular load may comprise large and small particles of a relatively wide size range. Still further, any particular load may comprise a combination of materials, such as sand and stone, both of either uniform or widely varying sizes. The device, therefore, has a very wide range of application, beinguseful to transfer practically any kind of solid material that maybe reduced to a size which the trough or pan can carry.

In Figs. 4 and 5 I have illustrated a preferred type of trough or pan construction. This trough has a body 30 with a supporting surface 3|. Side walls I are provided which with the supporting surface 3| provide a trough of substantially U- shaped cross-section. The trough has an open discharge end IM and a closed rear or feed end I02.

Figs. 6 and 'I show another type of trough or pan which may be employed. This trough comprises a substantially semi-cylindrical body I03, being otherwise substantially the same as the trough illustrated in Figs. 4 and 5.

Figs. 8, 9 and 10 illustrate still another type of trough or pan which comprises essentially a cylindrical body I04. At the feed end thereof an opening I05 is provided leading to a reception hopper or bin I06. This construction also differs from that of Figs. 4 and 5 or Figs. 6 and 7 in that the cantilevers are not bolted directly to the trough or pan but are bolted to straps I01 which in turn are rigidly clamped to the trough or pan I04, as by screws.

The improved method of transferring material herein disclosed is disclosed and claimed in my copending application Serial No. 57,910 filed January 7, 1936.

Obviously those skilled in the art may make various changes in the details and arrangement of parts without departing from the spirit and scope of the invention as defined by the claims hereto appended, and I wish therefore not to be restricted to the precise construction herein disclosed.

Having thus described and shown an embodiment of my invention, what I desire to secure by Letters Patent ofthe United States is:

1. In an electric motor, the combination with a field structure adapted to be energized by undulating fiux, of a plurality of adjacently disposed armatures one of which is free to vibrate with respect to said field structure, and means to position said field structure variably with respect to said armatures whereby said fiux may be variablydivided between said armatures.

2. An electric motor adapted to operate a conveyor trough and comprising a. field structure adapted to be energized by undulating fiux, a plurality of armatures disposed adjacent said field structure adapted to receive energy from said field when energized, one of said armatures being I mounted for vibration, the other being stationary,

and means to position said field structure variably with respect to said armatures whereby the relative amounts of energy received by said armatures may be adjusted.

3. In an electric motor, the combination with a base, of a field structure adapted to be energized by alternating current and attached to said base, a pair of non-rotary armatures associated with said field, there being means providing relative adjustment between said armatures and said field, said armatures being so positioned as to maintain a substantially constant reluctance of magnetic path for any position of adjustment of said armatures and field, whereby a constant exciting current will be drawn by said field while the energy delivered to one of said armatures is varied.

4. In a vibratory electric motor, the combination with a base, of afield structure pivotally attached to said base, a pair of armatures, and

-' means for pivoting said field structure whereby either one of said armatures is under the infiuence of said field structure while the other is substantially uninfiuenced thereby.

5. In a vibratory electric motor, the combination with a base, of a field structure adapted to be energized by alternating current and pivoted to said base, a pair of armatures adapted to cooperate with said field structure to maintain the reluctance of its magnetic path substantially constant for varying positions thereof, one of said armatures being substantially rigidly attached to said base and the other attached thereto for vibration, and means for adjusting the position or said armatures whereby the amplitude,

net having a magnetic coreand adjustably a'ttached to said frame, a pair or armatures positioned to cooperate with said core to form a magnetic path for said electro-magnet, means for adjusting said electro-magnet so that said core moves from one of said armatures to reduce the flux therein and moves toward the other armature to increase the flux therein, said armstures being positioned to maintain at a substantially constant value the energizing current of said electro-magnet for any position of ad- ,iustment thereof.

'7. In an electric vibratory motor, the combination with a frame, of an alternating current electro-magnet having a magnetic core with a base and legs, a pair of armatures positioned to cooperate with said legs to form a magnetic path for said electro-magnet, means for adjusting said core from a position where the major portion of the flux therein passes through one of said armatures to a position where it passes through the other, said armatures being positioned to maintain the exciting current for said electromagnet substantially constant for any position of adjustment of said core.

J s A. FLINT. 

